The present invention relates to a thrust reverser for a turbofan-type turbojet engine having thrust reversing doors to redirect the airstream, more particularly such a thrust reverser having movable deflectors on the thrust reversing doors.
A turbofan-type turbojet engine comprises a primary exhaust flow duct extending coaxially with the longitudinal axis of the engine for exhausting the hot gases after passing through the turbine stages, and a secondary annular duct extending around the primary exhaust flow duct concentrically therewith to serve as an exhaust duct for the air flow generated by the turbofan. In such engines having a relatively high bypass ratio, the thrust reversing system may be applied solely to the air flow passing through the secondary annular duct. Due to the relatively high bypass ratio, the deflection of these gases in a direction having a forward component will provide a sufficient thrust reversing effect.
Thrust reversing devices are also well known in the art and may comprise one or more thrust reversing doors pivotally attached to the annular wall forming the secondary duct. The doors are movable between a retracted position, in which the outer surface of the door is substantially flush with the outer surface of the secondary duct and in which the air passing through the annular duct is unimpeded by the door.
Actuating means are provided to pivot the door such that an upstream edge is moved radially outwardly while a downstream edge is moved radially inwardly such that all or a large portion of the air passing through the secondary duct is deflected through a laterally facing opening in the annular wall forming the duct. The air directed through this opening has a forward acting component to supply the requisite reverse thrust.
A typical secondary annular duct having a thrust reversing system is illustrated in FIGS. 1 and 2, the annular duct comprising a fixed upstream portion 1, a thrust reversing system 2 and a fixed rear collar portion 3. The fixed upstream portion 1 comprises an outer panel 4, which defines an outer air flow surface, and an inner panel 5 which defines the outer boundary of the annular passage through which the air from the turbofan passes. This annular passage is defined between the inner surface 5 of the secondary duct and the wall 50 (See FIG. 9) of the primary, hot gas flow duct. An upstream frame 6 interconnects the outer panel 4 and the inner panel 5, and provides a mounting point for the door actuator 7a. Typically such actuator comprises a cylinder with an extendable and retractable piston rod connected to the thrust reversing door 7. Door 7 is pivotally attached to the annular duct such that, as the piston rod is extended, the upstream edge of the door 7 (toward the left as viewed in FIG. 1) moves radially outwardly, while the downstream edge of the door moves radially inwardly so as to uncover a laterally facing opening through the annular duct. The doors 7 are shown in their extended positions in FIG. 2.
Depending upon the specific application of the turbofan engine, any number of such thrust reversing doors may be utilized.
The inner surface of the thrust reversing doors 7 may have an indentation 7b, illustrated in FIG. 2, to provide space for the actuator 7a when the doors 7 are in the retracted position, as illustrated in FIG. 1.
The passage of the air through the laterally facing opening during reverse thrust operation is assisted by the deflection edge 8 formed as part of the inner panel 5. Each of the thrust reversing doors 7 comprises an outer panel 9 which, in the retracted position shown in FIG. 1, is substantially flush with outer surface of outer panel 4 to provide a continuous aerodynamic wall to facilitate the air flow indicated by arrow 10. Each door also has an inner panel 11 defining inner door surface and a structure 12 which may interconnect panels 9 and 11 and also provide a convenient attachment point for the actuator piston rod.
In order to maximize the efficiency of the thrust reverser, each thrust reversing door 7 has a deflector 13 affixed to its upstream edge. The deflectors 13 have portions which extend radially inwardly from the inner surface of the door defined by inner panel 11. When the doors are in their thrust reversing position, the deflectors 13 serve to impart a more forward direction to the air passing through the laterally facing opening, and, therefore serve to increase the efficiency of the thrust reverser.
The efficiency of the thrust reverser is also increased by orienting the inner panel 11 such that its upstream edge (left edge as viewed FIG. 1) is closer to the outer panel 9 than is the rear edge. While this serves to increase the efficiency of the device when the thrust reversing doors 7 are in their thrust reversing or extended positions, the inner panel 11 is radially displaced from the most efficient aerodynamic air flow surface, (indicated by dashed line 14 in FIG. 1) when the doors are in their closed positions. Line 14 corresponds to the most efficient aerodynamic air flow passing through the inner annular duct between the upstream fixed portion 1 and the downstream collar 3 indicated by arrow 15. By forming the inner surface of the inner panel 11 in the known fashion, a cavity 16 is defined between the inner panel 11 and the theoretical aerodynamic flow line 14. A portion of the flow 15 passes into the cavity 16 over the deflection edge 8 thereby causing air flow distortion and perturbations in the air flow, thereby reducing the aerodynamic efficiency of the system.
Other thrust reversing systems incorporating pivotable thrust reversing doors are shown in French Patent No. 2,559,838 and U.S. Pat. Nos. 4,485,970 to Fournier et al. and 4,410,152 to Kennedy et al. However, none of the prior art systems have resolved the problem of improving the air flow contour of the inner surface of the thrust reversing doors to match the ideal aerodynamic surface when the doors are in their closed positions. If the volume of the cavity 16 is reduced by moving the upstream edge of the inner panel 11 radially inwardly, the length of the deflector 13 extending beyond this surface is reduced, thereby reducing the efficiency of the device when the doors are in their thrust reversing positions.